Smokemeters



Dec. 27, 1960 L. HARTRIDGE SMOKEMETERS Filed April 28, 1959 3Sheets-Sheet 1 Inventor LESLIE HARTRI'DGE ZWMK Attorneys Dec. 27, 19601.. HARTRIDGE 2,966,092

' SMOKEMETERS Filed April 28, 1959 3 Sheets-Sheet z Inventor ESLIE HARTRiDGE Attorneys L. HARTRIDGE SMOKEMETERS Dec. 27, 1960 3 Sheets-Sheet3 Filed April 28, 1959 Inuehtor A Item eys N Ur SMOKEMETERS LeslieHartridge, Buckingham, England, assignor to Lesiie Hart-ridge Limited,Buckingham, England, a British company Filed Apr. 28, 1959, Ser. No.809,479

Gaims priority, application Great Britain Apr. 29, 1958 7 Claims. (Cl.8814) This invention has reference to improvements in and relating todevices, so-called smokemeters, for use in ascertaining the densities ofsmoke samples or for comparing the samples with a standard gas, such asair.

Smokemeters to which the invention relates comprise a chamber adapted tohave smoke introduced into it, the smoke preferably flowing continuouslyinto and out of the chamber, a source of illumination, a photoelectriccell adapted to receive light from the said source after it has passedthrough the smoke in the chamber and a micro-ammeter associated with thephotoelectric cell to give a reading commensurate with the intensitywith which the cell is illuminated by the light source; and saidsmokemeters preferably comprise a clean air reference chamber to theinterior of which the light-source and the photo-cell can be exposedalternatively to being exposed to the interior of the chamber into whichsmoke is introduced. Thus, when the smokemeter includes a clean airreference chamber the light-source and photo cell are alternatelyexposed to the interior thereof and to the smoke chamber so that themicroammeter reading resulting from the passage of light through thesmoke chamber can be compared with the reading obtained when the lightpasses to the photo-ceil through the reference chamber.

After smokemeters at present in use have been operating for a short timean inaccuracy is introduced into the smoke density reading owing (a) tomoisture in the smoke condensing on the inner surface of the chamberand, by reflection, increasing the amount of light which strikes thecell by an amount in excess of that which would reach the cell were thesaid surface dry and (b) to the deposition of soot particles on thesurface of the chamber which reduces the amount or light reaching thecell; and these factors when present together cannot be relied upon tobalance each other out because each is a variable. Lagging the materialdefining the chamber and feeding the smoke at elevated temperature tothe chamber partialiy overcomes the objection arising out ofmoisturecondensa'tion on the surface of the chamber but the obis nonarising out of soot-.oepc-sitlon can only be satisfactorily overcome byfrequent cleaning of the surface of the chamber.

The principal object of the present invention is the provision of asmoikemeter wherein the effect of factors a and b above referred to isfor all practical purposes nullified by substantially confining thelight from the light source which strikes the photo-cell to lightpassing directly from the light source to the photo-cell. As a resultvaria- 2,9bfi92 Patented Dec. 27, 15960 tions of light intensity arisingout of increased or lessened reflectivity of the chamber walls aifectthe photo-cell output only after a prolonged period of use.

In accordance with the invention the internal surface of the chamberinto which smoke is introduced is provided at intervals along its lengthwith light barriers adapted to intercept light reflected by the saidsurface or by soot deposits on the said surface and so prevent thereflected light from reaching the photo-cell. Said light barriers form,in conjunction with the surface of the chamber, pockets in which sootcan collect before any light reflected by the soot can affect thereading of the milli-ammeter. Eventually of course the soot builds up toan extent such that the light barriers are unable to intercept thereflected light: at this stage cleaning or replacement of the chamber isnecessary.

In order that the said barriers shall not themselves present surfacesparallel with the axis of the tube from which reflection to thephoto-cell could take place, the inner peripheries of the barriers havesharp edges the extremities of which, therefore, have no appreciablearea.

The smoke chamber may be defined by a number of aligned elemental tubeseach having an annular flange directed towards the axis of the tube andterminating in a sharp edge. The material of which the said elementaltubes is made may be of any suitable kind, e.g., plastic or anodisedaluminium. Anodised aluminium is at present used because this materialhas been found to be reasonably resistant to corrosive acids containedin smoke.

Alternatively, the smoke chamber may be defined by a tube or tubes ofheat and acid resistant moisture-absorbent material provided withinternal ribs forming the light barriers. Suitable material is unglazedceramic ware or biscuit ware. The or each tube may comprise twosemi-cylindrical troughs arranged edge to edge.

When a smokemeter according to the invention comprises the clean airreference chamber, the reference chamber is preferably renderedoptically similar to the chamber into which smoke is introduced byproviding the reference chamber with barriers as previously set forth;such reference chamber may be provided by aligned elemental tubespreviously described or by the tube or tubes of heat and acid resistant,moisture-absorbent material with internal ribs as previously described.

The invention will now be described with reference to the accompanyingdrawings wherein:

Fig. i is a diagrammatic plan view of a smokemeter having a smokechamber and a reference chamber both provided by tubes and both providedwith internal batfles in accordance with the invention;

Fig. 2 is a front elevation of a constructional example of a smokemeterin accordance with the invention, parts of the device being shown insection;

Fig. 3 is a plan view thereof;

Figs. 4- and 5 are views from the left-hand end and righthand endrespectively of the said smokemeter;

Fig. 6 is a sectional plan view showing, more particularly, the tubesproviding the respective chambers and one way in which the tubes may bemounted;

Fig. 7 is a sectional elevation of a tubular unit built up from a numberof nested elemental tubes, four such units providing an alternative tothe tubes shown in g- Fig. 8 is an end view of the unit shown in Fig. 7;

Fig. 9 is a detail relating to the elemental tubes of Figs. 7 and 8;

Figs. 7 and 8 are to a larger scale than Figs, 2 to 6 and Fig. 9 is to aconsiderably larger scale than Figs. 7 and 8.

The smokemeter shown in Figs. 1 to 5, which is intended moreparticularly for use in ascertaining the density of the exhaust gases ofan internal combustion engine, comprises a main case 1 to the outerfaces of the end plates 2 and 3 of which end cover plates 4 and 5 ofdished form are secured by fixing screws 6 (best shown inFig.2).' r

A tube '7 adapted to receive a continuous flow'of smoke defines thesmoke chamber, indicated by 8; a tube 9 adapted to receive a continuousflow of clean air defines the clean air reference chamber, indicated by19. The ends of the tube 7 terminate short of the end plates 2 and 3opposite to holes 11 in the said plates; the ends of the tube 9 extendinto holes 12 in the end plates 2 and 3 and terminate at about the outerfaces of the plates. Smoke is introduced into the chamber 8 through aduct 13 at about the centre of' the chamber, said duct entering theinterior of the case 1 through the back wall thereof. Clean air isintroduced into the chamber at about the centre thereof through a duct14 communicating with the discharge passage 15 of a blower 16; theintake passage 17 of the blower receives clean air through an opening 18in the front of the case 1, which openings is covered by a gauze 19. Thecase 1 has outlet ducts 20 in the end plates 2 and 3.

An electric lamp 21 in the cover 4 provides the light source for thesmokemeter at one end of the tubes 7 and 9 whilst the photo-electriccell, indicated by 23, is located at the other end of the tubes in thecover 5. A shaft 24 which is supported in bearing bushes 25 on the endplates 2 and 3 with its axis equidistant from and below the axes of thesaid tubes has upwardly extending arms 26 rigid with it on which thelight source and the cell are mounted at such points that the axes ofthe source and cell, which are coincident, can be brought intocoincidence with the axis of either tube by swinging the arms on theaxis of the shaft. For this purpose a stub shaft 27 turnably supportedin a boss 28 on the end wall 29 of the cover 5 has a lever 30 secured toit at the end which projects outwardly from the said wall and has at itsother end, i.e., the end within the cover, an upwardly extending fork 31in the slot 32 of which is a pin 33 projecting laterally from the arm26. Thus forward and rearward movements of the lever 29 swing the armscorrespondingly so that the light source and the cell can be alignedwith either tube. Exact alignment is ensured by adjustable stops 34mounted on the end plate 3. The pin and slot connection 33-32 betweenthe lever 3i and the shaft 24 is to provide a readily disconnectible andre-connectiblecoupling between these elements when the cover 5 isremoved, to give access to the cell and, if required, to the tubes, andis replaced.

A micro-ammeter 35 connected to the photo-cell through a circuitcomprising a resistance36 is mounted on the case 1 at the front of themachine, said resistance having a contact 37 movable by means of a knob38 mounted in a panel 39 at the front of the said case. A convenientrange for the micro-ammeter is 0 to 100 microamps. The panel alsocarries a switch 40 for the light source and for an electric motor 41driving the blower .16 and carries a pilot lamp 42 in parallel with thelamp 21.

When a test is to be made the switch 40 is closed to energise the lightsource and the motor 41, the said source and the photo-electric cell areswung into alignment with the tube 9 and the resistance 36 is adjustedto bringthe micro-ammeter reading on the scale toapreselectedvalue.Smoke is then introduced into the smoke chamber 8 through the duct 13,by conducting the smoke to the duct through a pipe open to a smokestream, so

7 that the smoke passes continuously through the chamber from the middleto the ends thereof, and the light source and cell are swung intoalignment with the chamber 8 and the resulting micro-ammeter reading istaken. The smoke passes from the chamber 8 to the interior of the case 1and escapes therefrom through the ducts 20- which ducts may have hoseconnected to them for con ducting the smoke to a convenient dischargepoint. Air passing through the chamber 10 enters the interior of thecase]. by way of the hollows of the end covers 4 and 5 and the opening11 in the end plates 2 and 3 and escapes through the outlet ducts 20. rThe clean air flow is maintained throughout a test so that the airprovides barriers between the smoke issuing from the chamber 8 and thelight source and photo-cell. Also the air assists the passage of thesmoke towards the outlet ducts 20.

Soot or moisture deposition on the internal surface of the tube wouldseriously aflect the accuracy of the reading obtained in the test abovedescribed were provision not made to nullify the effect of suchdeposition.

In accordance with the principal feature of the present invention suchprovision resides in furnishing the interior surface of the tube 7defining the chamber 8 with a plurality of light barriers 43 whichintercept all light reflected or likely to be reflected by the interiorsurface of the tube so that whether the amount of reflected light belarge or small only light passing directly from the light source (i.e.without reflection) strikes the photo-cell. The light barriers 43 arealso deep enough to define pockets in which soot collects; hence theuseful life of the tube before cleaning is necessary is prolonged.

The said barriers may take any suitable form provided they act aseflicient interceptors of light which would otherwise be reflected or ofreflected light and do not themselves present surfaces parallel with theaxis of the tube from which reflection to the photo-cell could takeplace. This latter condition is satisfied according to the invention byproviding the inner peripheries of the barriers with sharp edges theextremities of which, therefore, have no appreciable area.

Two examples of construction of suitable tubes are shown in theaccompanying drawings. One of the examples, shown in Figs. 2, 3, 5 and6, comprises two similar aligned tubular units 7a, 7a each provided bytwo similar semi-cylindrical troughs 7b arranged edge to edge and ahollow cylindrical muff 44 between them, the hollow 45 of the cylinderbeing in alignment with the said units. The muff has a flange 46 on aneck portion 47 which flange enables the muff to be mounted in the case1 by means of screws 43 passing through a flange 49 on a connector 50outside the case and through holes in the Wall of the case and thence tothe flange 46. The connector and the flanged neck of the mulf define theduct 13. The troughs may be of any suitable material, preferably heatand acid resistant, moistureabsorbent material such as ceramic ware orbiscuit ware so that moisture contained in the smoke will be at leastpartly absorbed by the tube, and each has a plurality of equally spacedknife-edged ribs along its internal surface so positioned as to coincidewith the ribs on the other trough and thereby form the barriers 43. Thesharp edges of the barriers representing no appreciable area from whichlight can be reflected are indicated by 51, Fig. 6. 7

' The following test results illustrate the effectiveness of the saidlight barriers. In the tests smoke of uniform density was passed througha tube not provided with light barriers (Test 1) and through a tubeprovided with light barriers according to the invention (Test 2). The

micro-ammeter scale used in the tests was calibrated to show zero atfull photo-cell emission i.e., when the photo-cell was illuminatedthrough clean air and to show greater numerical readings as the cellemission decreased, said readings representing smoke density inarbitrary units compared with clean air. At zero cell emission themicro-ammeter read 100. Prior to each test the microammeter reading wasset to zero on the scale by means of the resistance.

Tube with light barriers Actual micro-ammeter reading taken during thesaid interval after tube had been cleared of smoke, show-rig that sootdeposited as dur ng Test 1 does not afiect microammeter reading Actualmicro-animator reading taken while smoke is introduced at intervals forperiods of 1 minute First Minute=24 +1 Minute =24. +1 Minute =24- +1Minute =24. +1 Minute =24- +1 Minute=24 +1 Minute=24 +1 Minute =24 +1Minute =24 +1 Minute =24- +1 Minute=24. +1 Minute=24 CG DOOOOQQOOO Theunits 7a, 7a above referred to are mounted within the case 1 ineasilyremovable and replaceable manner. For this purpose, the ends of theunits are chamfered at 52 and the ends of the muif have seats 53complementary to the chamfers on the adjacent ends of the units, and thechamfcrs at the ends of the units nearest to the end plates 2 and 3 arereceived in the complementary seats 54- in rings 55 which arespring-urged towards the muif. The mounting for each ring comprises afork 56 pivotally secured at its lower end to two blocks 57 by screws58, said blocks being fixed to the end plates 2 and 3 by screws 59. Thelower part of each ring lies between the limbs of the fork and the ringis pivotally attached to the limbs by screws 6!) diametrically oppositeto each other. Hence the pivoted forks and the screws 60 providemountings for the rings enabling the seats 54 to lie flush on thechamfers 52 with the rings in alignment with the units. The rings areurged into contact with the said chamfers by springs 61 between therespective end plates and the tops and bottoms of the rings, saidsprings being borne by pegs 62 projecting from the rings and enteringholes 63 in the end plates. Removal of the units thus requires thesimple operations of removing a detachable part of the casing andforcing the rings away from the units so that the latter can be lifted.Replacement is equally simple and the manner in which it is efiected isobvious.

In order that the reference chamber shall be optically similar to thechamber 8 it is formed of aligned units 9a similar in all respects tothe units 7a and of a muif 64 which is located between the aligned units9a and is substantially similar to the mufi 44. Mod 64 is integral withmuff 44 so it is held in position in the base by the screws 49 and likemufl 44 has seats 53 complementary to the chamfers 52 on the adjacentends of the units 9a. Duct 14 is formed in a hollow boss 65 with whichthe blower outlet 15 is connected. The chamfers 52 at the other ends ofthe units 94 bear against seats 66 at the ends of sleeves 67 which passthrough the holes 12 in the end plates and are secured to the end platesby screws 68 passing through flanges 69 on the sleeves, said sleevesproviding end extensions to the tubes which place the chamber 10 incommunication with the interior of the end covers 4 and 5.

The inner surface of the units 7a, 9a are preferably finished matt blackin order to assist suppression of reflected light.

The outlet ducts 20 for smoke and air in the constructional exampleshown are screw-threaded to facilitate the connection thereto of hoseand to take a cap nut 20a in the event of one outlet only being utilisedfor exhausting the smoke and air'from the case 1.

Smoke to be introduced into the chamber 8 is preferably first passedthrough a liquid trap 70 in order to reduce to some extent the moistureentering the chamber. The trap comprises a container 71 having a draincock 72 at its bottom and having a smoke inlet 73 and a smoke outlet 74near its top, a baffle 75 being located in the container between theinlet and the outlet. The outlet 74 is attached to the connector 50 bythe nut 76, Fig. 5.

It is desirable that the pressure of the smoke sensible at the ends ofthe tube 9 shall not be in excess of the pressure of the clean air.Otherwise the efiectiveness of the air barrier between the ends of thetube 7 and the light source and photo-cell would be impaired.Accordingly the smokemeter is provided with a smokepressure reliefvalve. Conveniently and as shown the relief valve is located at the topof the water trap. it comprises a hollow cylindrical extension 77 to thetop plate 7 8 of the liquid trap, in which extension is a weight 79normally resting on a seat 80 at the bottom of the hollow. The seatsurrounds a passage 81 between the interior of the trap and the hollowof the extension. The said extension 77 has an outlet connector 82 forhose (not shown). Smoke pressure above a predetermined maximum lifts theweight and smoke escapes through the connector 82. The valve may be ofspringloaded type instead of or as well as of weight-loaded type.

The second example of construction of tubes according to the inventionis built up from units of which one is shown in Figs. 7 and 8. The saidunit comprises a plurality of elemental tubes 86 and a tube 86a shorterthan the tubes 86. One end of each tube bends inwards to provide aflange 87 making an angle of about 45 with the tube axis Whilst theother end of each tube 86 is sharply enlarged to provide a shoulder 88near this end and a socket 89 at this end. The diameter of the socket issuch that it can receive the flanged end of a like tube or the flangedend of tube 86a, the extent of inward movement of the said end into thesocket being limited by the shoulder 88. Hence a number of tubes nestedin alignment as shown provide one unit containing a number of internallight barriers; and four such units can replace the units 7a and 9a,Figs. 2 to 6. The internal periphery of each flange 87 lies in a conecoaxial with the axis of the unit so that sharp edges 99 of noappreciable thickness corresponding to the sharp edges 51 of the units7a and 9a are presented to the interior of the unit. The material ofwhich the elemental tubes are made may be plastic, anodised aluminium orthe like.

I claim:

1. A smokemeter comprising means defining a chamber, said chamber havingopen ends, means for introducing smoke into said chamber, a source ofillumination located at one end of said chamber, a photoelectric cell,said photoelectric cell being located at that end of said chamberopposite to the end at which the source'of illumination is located, amicroammeter and an electrical connectionbetween said photoelectric celland said' ammeter, and light barriers in said chamber, said lightbarriers being located along said chamber on the inner surface thereofto intercept all light from said source other than light passingdirectly from said light source to said photoelectric cell, said lightbarriers being directed towards that axis of said chamber extending fromend to end thereof and having sharp edges opposite to said axis. A

- 2. A smokemeter as claimed in claim 1, wherein said chamber is definedby a plurality of elemental tubes, said tubes being in alignment witheach other and each having a flange directed towards its axis, the innerperiphery of said flange having a sharp edge.

3. A smokemeter as claimed in claim 1 comprising a hollow cylindricalmuff, the axis of said muff being coincident with said axis extendingfrom end to end of chamber, said mufi having a part defining asmokeentry duct, tubular elements abutting the muff at the ends thereofin alignment with the axis of said'mufi, said mufi and said tubularelements defining said, chamber, said tubular elements carrying saidlight barriers, and spring-loaded rings abutting the ends of the tubularelements furthest from the mufi, said rings being movable away'from thetubular elements to permit of easy removal of said elements from thesmokemeter and of easy replacement thereof.

4. A smokemeter comprising means defining a first chamber, said firstchamber being open at its ends, means defining a second chamber, saidsecond chamber being open at its ends, said second chamber being locatedalongside said first chamber substantially parallel to said firstchamber, a source of illumination'at one end of said chambers, aphotoelectric cell at the other end of said chambers, means movablysupporting said light source and means movably supporting saidphotoelectric cell permitting said source and said cell to be broughtselectively into alignment with said first chamber or with' said econdchamber at the open ends of said chambers, a microammeter and anelectrical connection between said photoelectric cell and saidmicroamrneter, means for introducing smoke into said first chamber andmeans for introducing clean air into said second chamber, and means forrendering the interiors of said chambers optically similar, said lastnamed means comprising light barriers in said chambers to intercept alllight passing through said chambers by way of the open ends thereofother than light passing through said chambers directly from said sourceto said photoelectric cell, said second chamber and said microammeterpermitting a comparison to be made between the intensity of direct lightreaching said photoelectric cell from said lamp when said direct lightpasses through clean air in said second chamber and the intensity ofdirect light reaching said photoelectric cell from said lamp when saiddirect light passes through said first chamber.

5. A smokemeter as claimed in claim' 4 wherein said light barriers arelocated along the respective chambers on the inner surfaces thereof andare directed towards the longitudinal axes of the respective chambers,said axes being the axes which pass through the open ends of thechambers, said light barriers having sharp edges opposite to said axes.

6. A smokemeter as claimed in claim 4 comprising a first hollowcylindrical muff and a second hollow cylindrical mufi, the axis of saidfirst muff being coincident with that axis extending from end to end ofsaid first chamber and the axis of said second mufi being coincidentwith that axis extending from end to end of said second chamber, saidfirst muff having a part defining a smoke-entry duct, said second muffhaving a part defining a clean air entry duct, tubular elements abuttingthe respective muffs at the ends of said mufis, said tubular elementsbeing in alignment with the respective muffs, said first muff and saidtubular elements abutting said first muff defining said first chamberand said second muff and said tubular elements abutting said second muffdefining said second chamber, said light barriers being mounted on saidtubular elements, and spring-loaded rings abutting the ends of thetubular elements furthest from the respective muffs, said rings beingmovable away from the respective tubular elements which they abut topermit of easy removal of said tubular elements from said smokemeter andof easy replacement thereof.

7. A smokemeter as claimed in claim 4, said means" References Cited inthe file of this patent UNITED STATES PATENTS Cahusac et a1 July 4, 1950Presenz Oct. 6, 1953

